Itraconazole, a triazole compound, is known to have excellent antifungal activity. However, the bioavailability of orally administered itraconazole is very low because it has a very low solubility of less than 1 .mu.g/ml in water and it remains unionized in the gastric juice due to its pKa value of 3.7. Further, it is known that the degree of bioavailability of orally administered itraconazole varies widely among individuals and depends on other factors such ingested foods.
PCT International Publication No. WO 85/02767 and U.S. Pat. No. 4,764,604 teach a method for increasing the solubility of itraconazole by employing a cyclodextrin inclusion compound of itraconazole. However, this method has the problems that the incremental increase in the itraconazole solubility is only marginal and various complicated preparative procedures are required.
Recently, PCT International Publication No. WO 94/05263 discloses a coated bead preparation, wherein a core made of pharmaceutically inert or neutral sucrose, dextrine, starch and the like is coated with a mixture of itraconazole and a hydrophilic polymer and, then, the resulting bead is coated again with a polymer, e.g., polyethylene glycol. Such a coated bead preparation is commercially available from Janssen Pharmaceutica(Beerse, Belgium) under the trade name of Sporanox.RTM. capsule. However, the manufacturing process of the above preparation is very complicated due to the fact the beads having an average size of only 600 to 700 .mu.m tend to undergo agglomeration during the manufacturing process.
PCT International Publication No. WO 97/44014 teaches a solid dispersion of itraconazole in a water-soluble polymer, which is prepared by subjecting a mixture of itraconazole and the water-soluble polymer to a melt-extrusion process at a temperature ranging from 245.degree. C. to 265.degree. C. This solid dispersion is described to have an improved bioavailability of itraconazole which is not influenced by ingested foods, and it is commercially available from Janssen Pharmaceutica(Beerse, Belgium) under the trade name of Sporanox.RTM. tablet. However, the manufacturing process of the solid dispersion is hampered by a number of difficulties in controlling various process variables, and the in vivo bioavailability of itraconazole achievable with the above dispersion is still low.
Accordingly, there has existed a need to develop an oral composition having improved in vivo bioavailability of itraconazole.